It is well known that arrhythmias such as ventricular fibrillation, can be reversed by passing high energy electric current through the fibrillating myocardium. This can be accomplished by means of external chest paddles placed on the patient's thorax in a hospital coronary care unit, or by electrodes applied directly to the surface of the heart in open heart surgery. Ventricular defibrillation can also be accomplished by using permanently implanted electrodes.
Already known is a catheter electrode system having two discrete conductive electrodes (or electrode sets) on a single implantable catheter. During defibrillation, an electrical field is established between the two electrodes on the catheter, and defibrillation is effected by depolarizing a critical mass of the myocardium. By so depolarizing this critical mass, the heart is brought back to normal cardiac rhythm. A bipolar catheter electrode is shown in commonly assigned U.S. Pat. No. 3,942,536.
Use of the bipolar catheter electrode reduces the energy requirements associated with external paddle defibrillation. Another effective low-energy approach to defibrillation through implanted electrodes is shown in commonly assigned U.S. Pat. No. 4,030,509. In this patent, defibrillation is accomplished by a conformal apex electrode which acts against, for example, a catheter electrode situated high in the heart or in the superior vena cava.
The bipolar catheter electrode shown in U.S. Pat. No. 3,942,536 comprises an electrically conductive lead molded in a silicone rubber casing wherein each of two electrodes is comprised of a plurality of spaced, conductive low impedance rings. The conductive electrode of the catheter shown in U.S. Pat. No. 4,030,509 is illustrated in a similar manner. This catheter electrode design, which is typical of the state of the art, is adequate. However, there is room for improvement in the design of the defibrillating catheter electrode.
Because of its being permanently implanted in a heart, any catheter electrode, whether bipolar or monopolar, must be capable of withstanding repeated lateral and axial flexing as well as momentary elongation, all over long periods of time. In addition, the electrode must have a relatively large surface area in order to efficiently discharge high amounts of energy for effective defibrillation, and must of course maintain its electrical integrity. The catheter electrode must also be biocompatible, that is, of biocompatible materials, as well as of a configuration having a smooth exterior surface to avoid tissue damage and to avoid the formation of clots. It is the object of the present invention to provide just such an electrode.